Method of manufacturing a magnetic head

ABSTRACT

A very precise method of manufacturing multiple magnetic heads which are to write, read and/or erase extremely narrow (&lt;0.2 mm.) tracks situated beside each other, for example, video heads or &#39;&#39;&#39;&#39;tunnel-erase&#39;&#39;&#39;&#39; heads. For that purpose very shallow (200-300 Mu ) parallel pairs of channels are sawn in a &#39;&#39;&#39;&#39;sandwich&#39;&#39;&#39;&#39; consisting of two plates of ferrite combined by means of glass which channels are afterwards filled with glass. Deeper (1 mm.) sawcuts are then provided in the conventional manner between the pairs of channels mutually and filled with nonmagnetizable intermediate members.

United States Patent .laeobus Pieter Beun; Jules Bos; George Ludwig Walther, all of Emmasingel, Eindhoven, Netherlands Inventors Appl. NO. 850,546

Filed Aug. 15, 1969 Patented July 20, 1971 Assignee U.S. Philips Corporation New York, N.Y.

Priority Aug. 22, 1968 Netherlands 681 1950 METHOD OF MANUFACTURING A MAGNETIC HEAD 4 Claims, 4 Drawing Figs.

US. Cl 29/603, 179/ 100.2 C

Int. Cl HOlf 7/06 Field of Search 29/603;

l79/l00.2 C; 346/74 MC; 340/1741 F [56] References Cited UNITED STATES PATENTS 3,384,954 5/ l 968 Bradford et al 29/603 3,402,463 9/1968 Bos et al. 29/603 3,474,528 10/1969 Walther et al. 29/603 Primary Examiner-John F. Campbell Assistant ExaminerCarl E. Hall Attorney-Frank R. Trifari ABSTRACT: A very precise method of manufacturing multiple magnetic heads which are to write, read and/or erase extremely narrow 0.2 mm.) tracks situated beside each other, for example, video heads or tunnel-erase" heads. For that purpose very shallow (200300 parallel pairs of channels are sawn in a sandwich" consisting of two plates of ferrite combined by means of glass which channels are afterwards filled with glass. Deeper (1 mm.) sawcuts are then provided in the conventional manner between the pairs of channels mutually and filled with nonmagnetizable intermediate members.

PATENTEH JULZO 19m SHEET 1 [1F 2 JACOBUS P. E W JULES BOS GEORGE L. WALTHER BY v AGENK PATENTEDJULZOIBL' 3,593,414

SHEET 2 [1F 2 INVENTOR5 JACOBUS R BEUN JULES 808 B EORGE Lv WALTHER ELM m a;

AGEN

f.'ivna'rrionol -mu tnulcruiuNo Aiivmcrinrrc'naAD I i Theinvention relates to a method of manufacturing-amagnetic head;for-recording,' pIaying-'and/or erasing records on a magnetiaable' carrier, the; magnetic' circuit(s of which consi'st(s-).of sinteredoxidic.ferromagneticmaterial comprising at least one operative gap filled withia nonmagnetizablemateriah H thestarting materiaI being sintered oxidieierromagnetic material which comprises a gap which is filledwith nonmag- "distance between-the gap-limiting surfaceseqhal to the ultimately desired gap length(s),' mutually vparallel saw cuts the' directionof which encloses an angle which is unequal to with the gap-limiting surfaces, which intersectthe gap and determinethe-distance between the-operative gaps belng'providedat mutual distances' corresponding to the:desired gap width('s) and beingfilledwith.a:nonmagnetizable'material. v Such'a methodofmanufacturingamagnetichead is known.

This method presented no problems in magncticheads'having 7 gap. widths exceeding 0.5 mm. However, for heads which are to write, read and/or erase very narrow-magnetic tracks-,rfor

example video: heads or tunnel: erase" heads,- the known method has great drawbacks. Actually-,if in-orde'r to obtaina' ,very narrow gap which'dcorresponds-tosuch 'verynar-ro'w tracks, ,channeis are formed'at very small distance fromteach' oth i-and witha depth of, for iexa mple, l"mm. or more, a'very narrowlandgcomparatively i high: upright edge remainswhich both during sawing andin: the further processingv can easily breakofior jcrumblelaway, the more'so=sincetthen1aterialto be processed, ferritepis very.brittler Thereexist severaltypes of 'miiltiple ma'gnetic. headsthe distances of which between successive operative j gapsare; considerably larger than 1 the gap 3 widths; This configuration .is obtained according to the method-already mentioned-inthatewidej channelsfimwhichan intermediate member: isprovided afterwards,- are; sawn' such thatwery narrowupright rims-oi 'fer'rite' remain:v (Such anin'te'r mediatejmembenmay consist; for example,,of*a"plate or a packet; which is nonmagnetizable at least: in the: direction at v rightsangles -tothe-:gap-lengthand whichserveslfor the mutual i screeninglofadjacentmagnetic CircuitsaSuch an intermediate member may also serve, forexample; for the mechanical'reim forcement'of the ,ultimate head, a in: particular there where? a l material-lobe used for theintermediate. member, thegreat:

danger existsthat said narrow--rims"may get-cracked when netizabl'em'aterial andfhas adepth at least equal to th'e'height' e f. th; l i g l d i d; iv gap or gaps, and either side of each gapto' be manufactured viewed in the relaflu's hwith the operative face ultimate head, after which,

in known manner, the operative face is provided, the parts of 300p) sawn' by meansof a veryfine sawing-operation on tive direction'of movement with theirespect to the magnetizable cairier', which" channels are afterwards filledwith a how magnetizable' material, magnetic headscan' be manufactured 1 the magnetic reluctance of which in the-proximity of the operative gap is verymuch larger "than anywhere else'in the very'small so'thatthe danger of breakingior" crumbling away bothduring' sawing and-during further processing is small as compared with the 'dangerwhicheitists when 'theconventional' methodof manufacturing'heads having'averysmall gap width isusedinwhichimmediatelydeepfior example, 1 mm.)chant I i nels-fwhichare to be filled withintermediate members are sawn betweenthe-gaps to be'ma'mifactured;

Since according :to the'invention deeper saw cuts'for the intermediatemembers; are provided betwee'n the shallow pairs of channels by means'f-of a secondzsawingoperation," channels" and'upri'ght rims are obtained which'are-considerably narrower and considerably wider; respectively, than thosewhich maintained; A further advantage; of the methodaccording to are obtain'ed by means of the conventional method', while nevertheless the ,requireddistance of the operative gaps is the invention 'isthat-the abovc-mentioned'danger of cracking Y of the uprightedgesofferi'ite is considerably rediiced not only support-of nonmagnetizable' material: is' necessary 'oneither during; sawing-but also during 1 cementing-the intermediate .members. H v v I Although-itis possible to provide nonmagnetiz'a'ble filling materialinthe pairs of channels'(t'orexamplqglass,which is first heated to-the melting temperature jandthen cooled) before the.sawing,of'the'deeper-channels'and the cementing of the intermediate members therein; them'ethod according to the. invention" provides an" additional advantage when the Q deeperch'annels are sewn, the intermediate'me'rnbers'are then Iaidin-them;so that they project above the bottom of thepairs of shallowchannels','fglass is provided insaidpairs ofchannels and then melted. The'melted glass will findits'way between thewalls ofthe intermediate membersand the deep channels.

comparatively large intermediate members are cemented-in the channels. Theinvention-solves thestructuraldifi'iculties inmanufac-- turing a 'magneticshead'as describedfabove, for which purpose 1 themethod according to the: inventiomis characterizedin tha't' the saw, cuts in; the: magnetizable 1 material 1 are: provided: by'

meansof'a first sawing operation; wherein=pairs'of'chan nels aresawn'iat least up to' the loweredge of thesmallest'gap-limit ing-surface present in -the.:finished head} in such mannerthat v I ,'the-gap:width(s)is (are) determinedzby-the'distanee(s) of the" channels-50f; one-pair and -in 1- such': manner that the? distance J between two'operative: gaps, is determinedrby' the distance of 7 i removedby meansaof a: second sawing'operation up to a depth exceeding the depth of thepairs'of channels formed by means" of thevfirst sawingoperationwhich are 'filled with' a nonmag-' netizable material the? mechanical properties of which are as much: as-possiblethrsame as those-ofthesintered oxidic ferwhen theassembly'is then'cooled, the intermediate members .will be cementedin'the 'channels'andthe glasswill be'provided in the'pairsof-channels.

pair 'of channels in'oneoperation-by meansofa double saw (that is to-say-with-two parallelsawing'tools) so that the distance between the-channelsisfixed, the gap width is reproducible. in this ma'nnerit is also possible, forexample, to use'a triple 'saw' in manufacturing tunnel-erase heads.

Pole shoe 1 units for' single and/or"multiple heads are ob- I tained-bysawingthe body, comprising theoperative gaps, after having-'ground it down, along planes'wh'ich' are situated'in the intermediate members preferably atright angles to the direction of=the gap width: In the'po'le' shoe 'unit of a multiple head, the parts of-adjacentbircuitscomprising the operative gaps may-then beseparated magnetically from each other by romagnetic material; and that the saw cuts obtained by 'means ,of-therse cond. sawingoperationarerfilled .withran intermediate v memberisuch'zthatthes upper lace rofisaidsmember 'is at least sawing the 'unit'along a plane which-touches or intersects the intermediate membersand which is preferably parallel to the operative face.

However, it is alternatively possible to separate the parts of adjacentcircuitfimagnetically from each-other by providing saw. cuts frombelow-in the'assembly'obtained' which saw'cuts' extend in the interm'ediate members:

'l'hemethod-accordin'g to the invention is of particular ad} vantage for series production: Since it is possible to saw one Finally the required wire turns may be provided and the magnetic circuits may be closed by means of magnetizable closing yokes or closing plates.

Although as a method of obtaining the pairs of channels in the above a sawing operation has been mentioned, it will be obvious that other methods, for example, polishing may alternatively be used.

An advantage of the method described over many of the so far known methods is that the size precision with respect to the gap width is provided in an initial stage of the total manufacture, which provides the advantage that a workpiece which does not correspond to the tolerances as regards the gap width, can be withdrawn from the production process before it has undergone the time-consuming subsequent operations.

A preferred embodiment of the method according to the invention is characterized in that pairs of channels are provided by means of a first sawing operation at such a mutual distance between the channels of one pair that in the finished head the operative gap has a width smaller than 0.2 mm. In the present video heads gap widths narrower than 0.2 mm. are conventional. During the actual manufacturing of heads with such small gap widths the possibility of breaking of the upright rims is large when one of the so far known methods is used.

A further preferred embodiment of the method according to the invention is characterized in that glass is used as a filling material for the pairs of channels. An advantage of glass is that it can be chosen to be so that in the relevant temperature range, themechanical properties are substantially equal to those of the ferrite used and that it can be provided by heating it to the melting temperature and then cooling it, while a type of glass may be chosen which has a melting temperature lower than that of the gap-filling material already present. Moreover, it is simple by means of the method according to the invention to provide the glass on either side of such a very narrow gap, and hence of a very narrow upright edge.

A further preferred embodiment of the method according to the invention is characterized in that the glass is provided in the pairs of channels and the intermediate members are provided in the saw cuts in one cementing process. One cementing process has the advantage that it provides a time saving which is of great importance for series production. Moreover, the coherence of the construction is better maintained when one cementing process is used than when two successive cementing processes are carried out.

The invention also relates to a magnetic head manufactured according to one or more of the above-mentioned methods.

In order that the invention may be readily carried into effect, one embodiment of the method according to the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which FIG. 1 is an isometric side-elevation of a pole shoe unit of a multiple magnetic head according to the invention in a stage of manufacturing succeeding the provision by means of a first sawing operation of shallow pairs of channels detemiining the gap width.

FIG. 2 shows the same pole shoe unit in a stage of manufacturing succeeding the provision of separate deep channels for the intermediate members by means of a second sawing operation.

FIG. 3 shows the same pole shoe unit in a stage of manufacturing succeeding the provision of nonmagnetizable material in the pairs of channels and of intermediate members in the individual channels.

FIG. 4 is a pole shoe unit of a multiple magnetic head after the gap-containing part has been separated from the lower part of the body and the operative face has been provided.

In the Figures, corresponding components have been given the same reference numerals.

In FIG. 1, blocks 1 and 2 of sintered oxidic ferromagnetic material are combined by means of nonmagnetizable material 3 having a thickness equal to the length of the gap in the finished head. (It is also possible to start from one block sintered oxidic ferromagnetic material which comprises a gap filled with nonmagnetizable material.) In the embodiment shown, 4 and 5 denote the surfaces which in the finished head form the gap-limiting surfaces. The two surfaces 4 and 5 comprise profiles 6 and 7, respectively, while the upper edge 8 of the profile 6 forms the reference line for determining the ultimately desired gap height.

In the body obtained by combining the blocks 1 and 2, shallow (200 to 300 1.) pairs of channels (9a, 9b) and (10a, 10b) are provided by means of a very finefirst sawing operation, said channels preferably being slightly deeper than the reference line 8 for the gap height. It is possible to saw pairs of channels in one operation by means of the above-mentioned double saw, so that the distance between the channels of one pair, which determines the gap width in the finished head, is reproducible. Very small gap widths namely smaller than 0.2 mm., can be obtained by means of a method of precision sawing, in which a saw" is used in the form of a disc which cuts throughout its circumference and is suspended and driven in a wobble-free manner, crumbling away of the ferrite being restricted to maximally 5 p..

In FIG. 2 reference numeral 11 denotes the saw cuts which are provided by means of a second sawing operation which may be coarser and is applied each time between adjacent pairs of channels 9 and 10 which saw cuts extend below the upper edge 8 of the profile 6.

Reference numerals 12 in FIG. 3 denote the nonmagnetizable filling material which is provided in the pairs of channels (90, 9b, 10a, 10b). The mechanical properties of this material 12 are as much as possible equal to those of the ferrite used. In the channels 1] nonmagnetizable material 13 is provided. This material 13 is to fill the channels II to such a height that in the finished pole shoe unit as shown in FIG. 4, it also forms the operative face, that is to say that it reaches up to or projects above the operative face to be formed ultimately. The filling material 12 and the bodies 13 are cemented separately or simultaneously in which in the latter case glass may be used as the filling material '12 which also serves as a cement for the bodies 13.

FIG. 4 shows a finished multiple pole shoe unit manufactured from a part of the structure shown in FIG. 3, after the operative face 14 has been given the desired shape by grinding down and the desireddistance d (gap height) up to the.

reference line 8 is reached and after the upper part of the structure has been separated from the lower part along the plane [3. Asa closing member may be used for each individual circuit, for example, a U-shaped circuit part (which circuit may be united previously to form one assembly by means of nonmagnetizable material) which can comprise the wire turns required for the head.

The above-described methods may also be of advantage for manufacturing a pole shoe unit ofa single magnetic head. Particularly there where a support 13a etc. of nonmagnetizable material is necessary on either side of the magnetic circuit parts so as to give the record carrier a larger supporting surface during operation.

What we claim is:

l. A method of manufacturing a magnetic head for recording, playing back erasing record on a magnetizable carrier, the magnetizable circuit of which consists of sintered oxidic ferromagnetic material comprising at least one operative gap filled with nonmagnetizable material, the starting material being sintered oxidic ferromagnetic material which comprises a gap which is filled with a nonmagnetizable material and has a depth of at least equal to the height of the ultimately desired operative gap or gaps, and with a distance between the gaplimiting surfaces equal to the ultimately desired gap length, mutually parallel saw cuts, the direction of which encloses an angle which is unequal to 0 with the gap-limiting surfaces, which intersect the gap and determine the distance between the operative gaps, being provided at mutual distances corresponding to the desired gap width and being filled with a nonmagnetizable material, characterized in that said saw cuts in the magnetizable material are provided by means of a first sawing operation, wherein pairs of channels are sawn at least up to the lower edge of the smallest gap-limiting surface present in the finished head, in such manner that the gap width is determined by the distance between the channels of one pair and in such manner that the distance between two operative gaps is determined by the distance between the innermost channels of two adjacent pairs of channels, that subsequently between the innermost channels of each set of adjacent pairs of channels the sintered oxidic ferromagnetic material is removed by means of a second sawing operation up to a depth exceeding the depth of the pairs of channels formed by means of the first sawing operation which pairs of channels are filled with nonmagnetizable material the mechanical properties of which are substantially the same as those of the sintered oxidic ferromagnetic material, and that the saw cuts obtained by means of the second sawing operation are filled with a member such that the upper face of said member is at least flush with the operative face of the ultimate head, after which,

- the operative face is provided, the parts of sintered oxidic ferromagnetic material comprising the operative gaps, and which in the finished head form the pole shoe units of two adjacent circuits are separated magnetically from each other by providing one or more saw cuts, the wire turns required for the head being provided and the magnetic circuits being finally closed.

2. A method as claimed in claim 1, characterized in that pairs of channels are provided by means of a first sawing operation at such a mutual distance between the channels of one pair that the operative gap in the finished head has a width smaller than 0.2 mm.

3. A method as claimed in claim 1, characterized in that the pairs of channels formed by means of the first sawing operation are filled with glass which has a melting point lower than that of the gap-filling material.

4. A method as claimed in claim 3, characterized in that the glass is provided in the pairs of channels formed by means of the first sawing operation and the intermediate members are provided in the saw cuts in one cementing process. 

1. A method of manufacturing a magnetic head for recording, playing back erasing record on a magnetizable carrier, the magnetizable circuit of which consists of sintered oxidic ferromagnetic material comprising at least one operative gap filled with nonmagnetizable material, the starting material being sintered oxidic ferromagnetic material which comprises a gap which is filled with a nonmagnetizable material and has a depth of at least equal to the height of the ultimately desired operative gap or gaps, and with a distance between the gaplimiting surfaces equal to the ultimately desired gap length, mutually parallel saw cuts, the direction of which encloses an angle which is unequal to 0* with the gap-limiting surfaces, which intersect the gap and determine the distance between the operative gaps, being provided at mutual distances corresponding to the desired gap width and being filled with a nonmagnetizable material, characterized in that said saw cuts in the magnetizable material are provided by means of a first sawing operation, wherein pairs of channels are sawn at least up to the lower edge of the smallest gap-limiting surface present in the finished head, in such manner that the gap width is determined by the distance between the channels of one pair and in such manner that the distance between two operative gaps is determined by the distance between the innermost channels of two adjacent pairs of channels, that subsequently between the innermost channels of each set of adjacent pairs of channels the sintered oxidic ferromagnetic material is removed by means of a second sawing operation up to a depth exceeding the depth of the pairs of channels formed by means of the first sawing operation which pairs of channels are filled with nonmagnetizable material the mechanical properties of which are substantially the same as those of the sintered oxidic ferromagnetic material, and that the saw cuts obtained by means of the second sawing operation are filled with a member such that the upper face of said member is at least flush with the operative face of the ultimate head, after which, the operative face is provided, the parts of sintered oxidic ferromagnetic material comprising the operative gaps, and which in the finished head form the pole shoe units of two adjacent circuits are separated magnetically from each other by providing one or more saw cuts, the wire turns required for the head being provided and the magnetic circuits being finally closed.
 2. A method as claimed in claim 1, characterized in that pairs of channels are provided by means of a first sawing operation at such a mutual distance between the channels of one pair that the operative gap in the finished head has a width smaller than 0.2 mm.
 3. A method as claimed in claim 1, characterizeD in that the pairs of channels formed by means of the first sawing operation are filled with glass which has a melting point lower than that of the gap-filling material.
 4. A method as claimed in claim 3, characterized in that the glass is provided in the pairs of channels formed by means of the first sawing operation and the intermediate members are provided in the saw cuts in one cementing process. 